LIMITATIONS OF A CALCULATED N MINERALIZATION POTENTIAL IN STUDIES OF THE N MINERALIZATION PROCESS

Soil is often incubated under controlled conditions to assess its capa city to mineralize nitrogen and to define the N mineralization potenti al (N-0) by fitting a negative exponential curve to N mineralization d ata. The specificity of N-0 for a given soil and its relevance in N mi neralization studies was examined as part of an overall study of the N mineralization process. Soil mixed with an equal amount of sand was a erobically incubated at 35 degrees C and leached at specific time inte rvals. Upon leaching, ammonium and nitrate were measured in the extrac t. It was found that N mineralization data did not always follow first -order kinetics making it difficult to calculate N-0. The computed N-0 value was influenced by the shape of the curve, the duration of the i ncubation experiment and was reciprocally related to the N mineralizat ion constant (k(exp)). N-0 did not always give an adequate indication of the amount of N mineralized and was not soil specific as the time o f sampling largely affected its size. The usefulness of N-0 in the sim ulation of the N mineralization process with a k(exp) value valid for all soils was limited and a k(exp) value specific for each soil was re quired. A value combining the soil specific N-0 and k(exp) values and reflecting the amount of N mineralized over one year was proposed as a suitable alternative to the use of N-0 in comparative studies of the N mineralization process. It was concluded that a calculated N-0 could not be used in studies comparing the N mineralization of different so ils. In addition, the simulation of the N mineralization required the use of the soil specific k(exp) and could not be carried out with a k( exp) valid for all soils.